U.S. patent number 7,168,333 [Application Number 10/226,217] was granted by the patent office on 2007-01-30 for monitoring system for pressurized container.
This patent grant is currently assigned to BS&B Safety Systems Limited. Invention is credited to Geof Brazier, John P. Clark, III, John E. Smallwood.
United States Patent |
7,168,333 |
Brazier , et al. |
January 30, 2007 |
Monitoring system for pressurized container
Abstract
A system and method of monitoring a pressurized container having
an auxiliary device are provided. The system includes a sensor
operable to provide a signal representative of at least one
operating condition of the pressurized container. The system also
includes a control operable to receive the signal from the sensor
and generate a warning when the sensed operating condition will
impact the operation of the auxiliary device.
Inventors: |
Brazier; Geof (Woodbury,
MN), Clark, III; John P. (Tulsa, OK), Smallwood; John
E. (Singapore, SG) |
Assignee: |
BS&B Safety Systems Limited
(Limerick, IE)
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Family
ID: |
23219367 |
Appl.
No.: |
10/226,217 |
Filed: |
August 23, 2002 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20030071736 A1 |
Apr 17, 2003 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60314291 |
Aug 24, 2001 |
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Current U.S.
Class: |
73/865.8;
137/552; 73/52; 73/862.382; 340/606; 340/603; 137/557; 137/551 |
Current CPC
Class: |
F17C
13/026 (20130101); F17C 13/02 (20130101); F16K
37/0091 (20130101); F16K 37/0083 (20130101); F17C
13/12 (20130101); G05B 23/0235 (20130101); F16K
17/1606 (20130101); F17C 2250/0473 (20130101); Y10T
137/8326 (20150401); F17C 2250/0404 (20130101); F17C
2250/0626 (20130101); F17C 2250/043 (20130101); F17C
2205/0332 (20130101); F17C 2250/0434 (20130101); F17C
2250/0408 (20130101); Y10T 137/8158 (20150401); F17C
2250/036 (20130101); F17C 2250/0491 (20130101); F17C
2260/022 (20130101); F17C 2250/032 (20130101); F17C
2250/077 (20130101); F17C 2205/0314 (20130101); F17C
2250/072 (20130101); F17C 2250/06 (20130101); F17C
2250/0439 (20130101); F17C 2223/0123 (20130101); F17C
2250/034 (20130101); F17C 2250/0465 (20130101); F17C
2250/075 (20130101); F17C 2260/016 (20130101); Y10T
137/8175 (20150401); F17C 2260/023 (20130101) |
Current International
Class: |
G08B
19/00 (20060101); G08B 23/00 (20060101) |
Field of
Search: |
;73/1.71,37,52
;137/15.11,551,552,557 ;340/603,605,606,611,626 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 092 323 |
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Oct 1983 |
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EP |
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0 400 818 |
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Dec 1990 |
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EP |
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Other References
International Search Report, dated Nov. 18, 2002. cited by
other.
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Primary Examiner: Williams; Hezron
Assistant Examiner: Rogers; David A.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner, L.L.P.
Parent Case Text
RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application
No. 60/314,291, filed on Aug. 24, 2001, which is expressly
incorporated herein by reference.
Claims
What is claimed is:
1. A monitoring system for a pressurized container having an
auxiliary device, the system comprising: a sensor operatively
disposed in the pressurized container to generate a signal
representing a direct measurement within the pressurized container
of at least one operating condition of the pressurized container,
the signal generated by the sensor being independent from and
unaffected by the condition of the auxiliary device; and a control
operably connected to the sensor and operable to receive the signal
and monitor the signal to generate a warning when the at least one
operating condition of the pressurized container system will
adversely impact the intended operation of the auxiliary
device.
2. The system of claim 1, wherein the auxiliary device is chosen
from the group including a pressure relief device, a pressure
reduction device, a pressure control device, a pressure indicating
device, and a pressure sensing device.
3. The system of claim 1, wherein the auxiliary device is a
pressure relief device and the signal is representative of a back
pressure exerted on the pressure relief device, and the warning is
generated when the back pressure exceeds a back pressure limit.
4. The system of claim 1, wherein the signal is representative of
the pH level, and the warning is generated when the pH level is
outside of a predetermined pH range appropriate for the proper
operation of the auxiliary device.
5. The system of claim 1, wherein the signal is representative of
the pressure of a fluid within the pressurized container.
6. The system of claim 5, wherein the system has a maximum
allowable working pressure and the warning is generated when the
pressure within the system exceeds a threshold that is a
predetermined percentage of the maximum allowable working
pressure.
7. The system of claim 6, wherein the threshold is approximately
105% of the maximum allowable working pressure.
8. The system of claim 1, wherein the signal is representative of
the temperature within the pressurized container.
9. The system of claim 8, wherein the warning is generated when the
temperature exceeds a first temperature limit.
10. The system of claim 8, wherein the warning is generated when
the temperature falls below a second temperature limit.
11. The system of claim 1, wherein the control includes a first
memory configured to store a series of signals received
representing a direct measurement within the pressurized container
of the at least one operating condition over a predetermined time
period.
12. The system of claim 11, further comprising a pressure event
sensor operable to generate an event signal when the auxiliary
device activates.
13. The system of claim 12, wherein the control includes a second
memory means, the control transferring the series of signals
received from the first memory to the second memory upon receipt of
a burst signal.
14. A method of monitoring conditions experienced by a pressurized
container having an auxiliary device, the method comprising the
steps of: sensing at least one operating condition of the
pressurized container; generating a signal representing a direct
measurement within the pressurized container of the at least one
operating condition of the pressurized container; receiving the
signal; monitoring the signal; issuing a warning when the at least
one operating condition of the pressurized container will adversely
impact the intended operation of the auxiliary device; and wherein
the signal generated is independent from and unaffected by the
condition of the auxiliary device.
15. The method of claim 14, wherein the signal is representative of
a back pressure exerted on the auxiliary device, and the warning is
generated when the back pressure exceeds a back pressure limit.
16. The method of claim 14, wherein the signal is representative of
the pH level in the fluid, and the warning is generated when the pH
level is outside of a predetermined pH range.
17. The method of claim 14, wherein the auxiliary device is a
pressure relief device and further comprising: inputting a set of
performance characteristics of the pressure relief device into a
control; and comparing the at least one operating condition to at
least one of the performance characteristics of the pressure relief
device.
18. The method of claim 17, wherein the signal is representative of
the pressure within the pressurized container.
19. The method of claim 18, wherein the pressurized container has a
maximum allowable working pressure and the performance
characteristics of the pressure relief device include an operating
ratio and a rated pressure, and wherein the warning is generated
when the pressure within the system exceeds a threshold determined
by multiplying the operating ratio times the rated pressure of the
pressure relief device.
20. The method of claim 14, wherein the signal is representative of
the temperature within the pressurized container.
21. The method of claim 20, wherein the warning is generated when
the temperature exceeds an upper temperature limit.
22. The method of claim 21, wherein the warning is generated when
the temperature falls below a lower temperature limit.
23. A method of monitoring conditions experienced by a pressure
reduction device sealingly engaged in a pressurized container
having an auxiliary device, the method comprising the steps of:
receiving a series of signals representing a direct measurement
within the pressurized container of at least one operating
condition of the pressurized container, each of the signals
received representing a direct measurement of the operating
condition existing at a particular time; storing each signal in a
first memory; receiving a pressure event signal from a pressure
event sensor; transmitting a historical set of signals received to
a second memory, the historical set containing the signals received
during a predetermined time period immediately prior to receipt of
the pressure event signal; issuing a warning when the at least one
operating condition of the pressurized container will adversely
impact the intended operation of the auxiliary device; and wherein
the series of signals representing a direct measurement within the
pressurized container of at least one operating condition are
independent from and unaffected by the condition of the pressure
reduction device.
24. The method of claim 23, further comprising the deleting the
signals received from the first memory after the predetermined time
period has expired.
25. The method of claim 23, further comprising sensing the
operating conditions of the pressurized container prior to the step
of receiving a series of signals.
26. The method of claim 23, wherein the operating conditions
include the temperature within the pressurized container.
27. The method of claim 23, wherein the operating conditions
include the pressure within the pressurized container.
28. The method of claim 23, wherein the operating conditions
include the pH level within the pressurized container.
29. The method of claim 23, wherein the operating conditions
include a back pressure exerted on the pressure reduction
device.
30. The method of claim 23, wherein at least one sensor generates
the series of signals representing a direct measurement within the
pressurized container and the method further comprises sending an
interrogation signal to the at least one sensor to determine if the
at least one sensor is operational.
31. The method of claim 30, wherein the at least one sensor
provides a return signal responsive to the interrogation signal,
the return signal providing diagnostic information related to the
at least one sensor.
32. A monitoring system for a pressure reduction device sealingly
engaged in a pressurized container having an auxiliary device, the
system comprising: a pressure event sensor operable to generate an
event signal upon activation of the pressure reduction device; a
condition sensor disposed in the pressurized container and operable
to generate an operational signal representing a direct measurement
within the pressurized container of at least one operating
condition of the pressurized container for a particular time, the
operational signal generated by the condition sensor being
independent from and unaffected by the condition of the pressure
reduction device; a control operable to receive the signals from
the pressure event sensor and condition sensor, the control having
a first memory for storing a historical set of operational signals
representing a direct measurement within the pressurized container
of the at least one operating condition over a predetermined time
period and a second memory, the control transferring the historical
set of operational signals to the second memory upon receipt of the
event signal; and wherein the control is operably connected to the
condition sensor and operable to monitor the operational signal to
generate a warning when the at least one operating condition of the
pressurized container system will adversely impact the intended
operation of the auxiliary device.
33. The system of claim 32, wherein the operational signal is
representative of a back pressure exerted on the pressure reduction
device and the control generates an additional warning when the
back pressure exceeds a back pressure limit.
34. The system of claim 32, wherein the operational signal is
representative of the pH level and the control generates an
additional warning when the pH level is outside of a predetermined
pH range.
35. The system of claim 32, wherein the control is operable to
generate and send an interrogation signal to the condition sensor
to determine if the condition sensor is operational.
36. The system of claim 35, wherein the condition sensor is
operable to provide a return signal responsive to the interrogation
signal, the return signal providing diagnostic information related
to the condition sensor.
37. The system of claim 32, wherein the operational signal is
representative of the pressure within the pressurized
container.
38. The system of claim 37, wherein the system has a maximum
allowable working pressure and the control is operable to generate
an additional warning when the pressure within the system exceeds a
threshold that is a certain percentage of the maximum allowable
working pressure.
39. The system of claim 32, wherein the operational signal is
representative of the temperature within the pressurized
container.
40. The system of claim 39, wherein the control is operable to
generate an additional warning when the temperature exceeds an
upper temperature limit.
41. The system of claim 39, wherein the control is operable to
generate an additional warning when the temperature falls below a
lower temperature limit.
Description
BACKGROUND OF THE INVENTION
This invention generally relates to a method and system for
monitoring a pressurized container. More particularly, the present
invention relates to a monitoring system for a pressurized
container that includes a safety device or an information providing
device.
Containers, such as, for example, systems, piping, or tanks, that
contain a fluid that is pressurized or that may be pressurized
often include pressure reduction equipment that is designed to
ensure the safety of the container and/or to provide information
about the operation of the system. This pressure reduction
equipment may include, for example, pressure relief devices,
pressure release devices, pressure control systems, pressure
indicating devices, pressure driven switching devices, temperature
indicating devices, fluid pH level indicating devices, and
vibration indicating devices.
Pressure relief devices are commonly used as safety devices to
prevent fluid containers from experiencing potentially hazardous
over-pressure or under-pressure conditions. The pressure relief
devices are designed to activate, or open, when the pressure of the
fluid within the container reaches a predetermined pressure limit
that is indicative of an over-pressure condition. The activation of
the pressure relief device creates a vent path through which fluid
may escape to relieve the over-pressure situation in the
pressurized container.
A pressure relief device, which may include, for example, rupture
disks, pressure relief valves, pressure safety valves, control
valves, butterfly valves, gate valves, globe valves, diaphragm
valves, buckling pin devices, tank vents, explosion panels, or
other such devices, may be connected to the container so that at
least a portion of the pressure relief device is exposed to the
fluid within the container. When the fluid reaches or exceeds the
predetermined pressure limit, the force of the fluid on the
pressure relief device acts on the pressure relief device to
activate the pressure relief device, thereby creating an opening.
Fluid may then escape from the container through the opening to
relieve the over-pressure condition.
Pressure release devices are commonly used to allow the movement of
a pressurized fluid from one container to another container or
system. The pressure release devices, which may be, for example,
control valves, butterfly valves, gate valves, globe valves, ball
valves, diaphragm valves, or other such devices, are connected to
the container so that at least a portion of the pressure release
device is exposed to the fluid within the container. The pressure
release devices are designed to activate, or open, on demand. This
activation can be manual or automatic, based upon the requirements
of the user. When fluid is required to be discharged from the
container, the pressure release device may be activated to create
an opening. The activation of the pressure release device creates a
vent path through which fluid may escape from the pressurized
container.
A combination of different types of pressure reduction equipment
may be included in a container. For example, a pressure relief
device may be engaged with the system to provide protection from an
over pressure situation within the particular container. A pressure
release device may be engaged with the container to allow the
discharge of fluid from the container upon the command of an
operator or an appropriate automatic sensing system when certain
internal or external conditions are experienced that warrant
discharge of the pressurized fluid from the container.
Each pressurized container is designed to withstand a maximum
allowable working pressure. If the pressure of the fluid within the
container were to exceed this maximum allowable working pressure
without activation of the pressure reduction device, the container
could become unsafe. To ensure that the pressure of the container
does not exceed the maximum allowable working pressure and the
relevant design code permitted overpressure, a pressure reduction
device that is configured to activate at a pressure that is within
a certain tolerance (e.g. 105%) of the maximum allowable working
pressure may be engaged in the container.
Ensuring that the pressure reduction equipment activates at the
rated pressure, or within a manufacturing tolerance of the rated
pressure, is of great importance. If the pressure reduction device
activates at a pressure that is higher than the rated pressure, the
fluid pressure may exceed the maximum allowable working pressure.
If the pressure reduction device activates at a pressure that is
lower than the rated pressure, the activation may interfere with
the normal operation of the system and could potentially result in
the premature loss of fluid from the system.
The pressurized containers may further include a pressure control
system that is designed to prevent the pressurized container from
experiencing potentially hazardous over-pressure or under-pressure
conditions. These pressure control systems monitor the pressure of
the fluid within the container. When the fluid pressure approaches
a predetermined pressure limit that is indicative of an impending
over-pressure or under-pressure condition, the pressure control
system may activate a control device, such as, for example, a
control valve that injects a chemical reaction agent, catalyst,
quenching agent, or stabilizer into the working fluid. The
activation of the pressure control system may thereby avoid the
need to create a vent path to reduce the pressure of the fluid in
the pressurized system. Alternatively, the pressure control system
may activate a pressure release device, such as, for example, a
butterfly valve, a ball valve, or a globe valve, to release fluid
in a sufficient quantity to avoid or limit the over-pressure or
under-pressure condition. Thus, the control system may
automatically handle the opening and closing of a vent path in a
pressure release device to reduce the pressure within the
container.
The pressurized containers may use a combination of pressure
control devices and pressure reduction devices. These pressure
control devices monitor the pressure of the fluid within the
container. When the fluid pressure reaches a level that may be too
low or too high for the proper function of the pressure release
device, the pressure control system may activate an annunciation
system to alert the user to the improper operating condition of the
pressurized container. A pressure relief device may additionally be
used to provide automatic release of fluid in a sufficient quantity
to avoid or limit an overpressure or under-pressure condition.
The pressurized containers may also include a pressure indicating
device that identifies the depletion of the fluid within the
container. These pressure indicating devices can be used to prevent
the containers from experiencing potentially low or high pressure
conditions that might inconvenience the user. The pressure
indicating devices are designed to trigger a response, such as the
opening of a supply valve, when the pressure of the fluid within
the system reaches a predetermined low pressure limit that is
indicative of the fluid becoming depleted. Such pressure indication
can also trigger a response when the pressurized container is
reaching a potentially damaging vacuum condition.
The pressurized containers may further include a pressure
indicating device that identifies the increase in quantity of the
fluid within the container. These pressure indicating devices can
prevent the containers from experiencing potentially high pressure
conditions that might damage the container. The pressure indicating
devices are designed to trigger a response, such as, for example,
the opening or closing of a supply valve, when the pressure of the
fluid within the system reaches a predetermined pressure limit that
is indicative of the system becoming filled with fluid.
It has been found that the operating conditions of the fluid
container, such as, for example, the temperature and pressure of
the fluid, may have an impact on the operation of the
above-described pressure reduction devices and information
providing devices that may be engaged with the container. For
example, the operating conditions of the container may have an
impact on the pressure at which a pressure relief device activates.
In some situations, the operating conditions of the container may
cause the pressure relief device to activate at a pressure that is
lower than expected. In other situations, the operating conditions
of the container may cause the pressure relief device to activate
at a pressure that is higher than expected.
In a container that uses a rupture disk as a pressure relief
device, the temperature of the fluid in the container may impact
the pressure at which the rupture disk will activate. The
activation pressure of the rupture disk is determined, in part, by
the physical properties of the material used to form to the rupture
disk. Excessive heat or excessive cold may alter the physical
properties of the material, thereby altering the activation
pressure of the rupture disk. Other operating conditions, such as,
for example, pressure fluctuations, pressure levels, vibration
frequencies and amplitudes, and acidity levels could also have an
impact on the activation pressure of the rupture disk or other such
pressure relief device.
Similarly, the operating conditions of the container may also
impact the operation of a pressure release device, a pressure
control device, and/or a pressure indicating device. For example,
excessive pressures or temperatures may impact the ability of a
pressure control device to deliver a stabilizing agent to a
chemical reaction process before an over-pressure condition is
reached. In addition, the operating conditions may prevent a
pressure indicating device from providing accurate pressure
indications.
Early identification of an operating condition that may impact the
operation of a pressurized container fluid system or an associated
pressure release devices, pressure relied device, and/or pressure
control device may allow an operator to take corrective action. For
example, the affected device could be repaired or replaced after
experiencing a potentially problematic operating condition. In this
manner, the reliability of the pressurized container fluid system
and the associated safety and informational systems could be
maintained.
In light of the foregoing, there is a need for a method and system
for monitoring the operating conditions experienced by a
pressurized container to identify conditions that may have an
impact on the operation of a pressure reduction device, a pressure
control system, and/or an information providing device that is
engaged with the container.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method and
system for monitoring operating conditions experienced by a
pressurized container and the associated pressure reduction
devices, pressure control systems, or information providing devices
that obviates one or more of the limitations and disadvantages of
prior art monitoring devices. The advantages and purposes of the
invention will be set forth in part in the description which
follows, and in part will be obvious from the description, or may
be learned by practice of the invention. The advantages and
purposes of the invention will be realized and attained by the
elements and combinations particularly pointed out in the appended
claims.
To attain the advantages and in accordance with the purposes of the
invention, as embodied and broadly described herein, the invention
is directed to a monitoring system for a pressurized container
having at least one auxiliary device. The system includes a sensor
that is operatively disposed in the pressurized system and
generates a monitoring signal representative of at least one
operating condition of the pressurized container. A control is
operably connected to the sensor and is operable to receive the
monitoring signal and to generate a warning when the at least one
operating condition of the pressurized container will impact the
operation of the auxiliary device.
In another aspect, the present invention is directed to a method of
monitoring conditions experienced by a pressurized container. At
least one operating condition of the pressurized container is
sensed. A monitoring signal representative of at least one
operating condition of the pressurized container is generated. The
monitoring signal is received. A warning is issued when the at
least one operating condition of the pressurized container will
impact the operation of the auxiliary device.
In still another aspect, the present invention is directed to a
method of monitoring conditions experienced by a pressure reduction
device that is sealingly engaged with a pressurized container. A
series of monitoring signals that are representative of at least
one operating condition of the pressurized container are received.
Each of the monitoring signals represent the operating condition
existing at a particular time. Each monitoring signal is stored in
a first memory. A pressure event signal is received from a pressure
event sensor. A historical set of monitoring signals are
transmitted to a second memory. The historical set contains the
monitoring signals received during a predetermined time period
immediately prior to receipt of the pressure event signal.
In yet another aspect, the present invention is directed to a
monitoring system for a pressure reduction device that is sealingly
engaged with a pressurized container. The system includes a
pressure event sensor operable to generate an event signal when a
significant pressure event is identified. A condition sensor is
disposed in the pressurized container and is operable to generate
an operational signal representative of at least one operating
condition of the pressurized container for a particular time. A
control is operable to receive the signals from the pressure event
sensor. The control has a first memory for storing a historical set
of operational signals representative of the at least one operating
condition over a predetermined time period and a second memory. The
control transfers the historical set of operational signals to the
second memory upon receipt of the event signal.
It is to be understood that both the foregoing general description
and the following detailed description are exemplary and
explanatory only and are not restrictive of the invention, as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute
a part of this specification, illustrate one embodiment of the
invention and together with the description, serve to explain the
principles of the invention. In the drawings,
FIG. 1 is a schematic and diagrammatic illustration of a monitoring
system for a pressurized container in accordance with an embodiment
of the present invention;
FIG. 2 is a schematic and diagrammatic illustration of one
embodiment of a monitoring system for a pressure relief device in
accordance with an embodiment of the present invention;
FIG. 3 is a schematic and diagrammatic illustration of a control
for a monitoring system according to an embodiment of the present
invention;
FIG. 4 is a flowchart illustrating a method of monitoring inlet
pressure conditions experienced by a pressure relief device in
accordance with an embodiment of the present invention;
FIG. 5 is a flowchart illustrating a method for monitoring inlet
and outlet pressure conditions experienced by a pressure relief
device in accordance with an embodiment of the present invention;
and
FIG. 6 is a flowchart illustrating a method for monitoring
temperature conditions experienced by a pressure relief device in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
Reference will now be made in detail to the presently preferred
embodiment of the present invention, an example of which is
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers will be used throughout the drawings to
refer to the same or like parts. An exemplary embodiment of a
monitoring system for a pressurized container is shown in FIG. 1
and is designated generally by reference number 10.
In accordance with the present invention, a monitoring system for a
pressurized container is provided. The monitoring system of the
present invention may be used with any pressurized container that
includes an auxiliary device, such as, for example, a safety
device, a pressure reduction device, a pressure control system, or
an information-providing device. Such pressure reduction devices
may include, for example, pressure relief devices and pressure
release devices. Such information-providing devices may include,
for example, pressure indicating devices and devices that indicate
when a container is full or empty.
As illustrated in FIG. 1, an auxiliary device 12 is engaged with a
container 11 that contains a pressurized fluid or a fluid that may
be pressurized. For the purposes of the present disclosure, the
term "container" is used broadly and is intended to include any
type of pressurized system, piping, tank, or other such apparatus.
Auxiliary device 12 is exposed to the fluid within container 11 so
that the auxiliary device may perform its intended function. For
example, auxiliary device 12 may be a pressure relief device that
is configured to activate, or open, when a fluid within the system
reaches a predetermined pressure level. The pressure relief device
may be, for example, a rupture disk, a pressure relief valve, a
pressure safety valve, a control valve, a buckling pin device, a
tank vent, an explosion panel, or another similar device.
Alternatively, auxiliary device 12 may be a pressure reduction
device that is configured to activate in response to an external
force. The pressure reduction device may activate manually in
response to a command from an operator or automatically in response
to a signal from an automatic control system. The pressure
reduction device may be activated when the operator or automatic
control system detects a condition that warrants release of fluid
from container 11.
As is known in the art, the pressure relief device may be engaged
with container 11 in any manner that will expose an operative
portion of the pressure relief device to the fluid contained within
container 11. When the fluid in the container reaches the
predetermined pressure level, the pressure relief device will
activate to create a vent path, or opening, through which fluid may
escape from the container to reduce the pressure in the container.
It is contemplated that multiple pressure relief devices may be
engaged at different locations within or adjacent container 11.
In the exemplary embodiment of the monitoring system illustrated in
FIG. 2, the auxiliary device 12 is a rupture disk 40. Rupture disk
40 is sealingly engaged between an inlet safety head 26 and an
outlet safety head 28. Inlet and outlet safety heads 26, 28 are
then secured between an inlet pipe 18 and an outlet pipe 19. The
present invention contemplates that rupture disk 40 may be engaged
with container 11 in any manner readily apparent to one skilled in
the art, such as, for example, between tri-clamp sanitary flanges,
between screw-threaded connections, welded to the container, or
directly between pipe flanges.
Inlet pipe 18 includes an inlet flange 24 and outlet pipe 19
includes an outlet flange 30. A series of bolts 22 secure inlet
flange 24 to outlet flange 30. When bolts 22 are tightened, a force
is exerted through inlet flange 24 and inlet safety head 26 and
outlet flange 30 and outlet safety head 28. This force sealingly
engages the rupture disk 40 with container 11.
In the embodiment of FIG. 2, inlet pipe 18 has an opening 32 that
provides a fluid pathway to rupture disk 40. Inlet safety head 26
includes an opening that exposes a rupturable portion of rupture
disk 40 to the fluid within container 11. The rupturable portion of
rupture disk 40 is configured to rupture when the pressure
differential across the rupturable portion of the rupture disk
reaches a predetermined limit. The rupture of rupture disk 40
creates a pathway through which fluid may escape from container
11.
Outlet pipe 19 has an opening 34 that provides a vent path for
fluid that escapes container 11 through the burst and therefore
open rupture disk. Outlet pipe 19 may lead to an overflow reservoir
(not shown). Alternatively, if the fluid within container 11 is not
hazardous, rupture disk 40 may vent directly to the environment or
outlet pipe 19 may direct the escaping fluid to the
environment.
With reference to FIG. 1, a sensor 14 is operatively disposed in
container 11 to monitor at least one operating condition of
container 11. It is contemplated, however, that multiple sensors
may be operatively disposed in container 11 and/or auxiliary device
12 to monitor several operating conditions simultaneously at the
inlet, outlet, or both the inlet and outlet of the device. The
monitored operating conditions may include, for example, inlet
pressure, outlet pressure, fluid temperature, fluid pH
level/acidity level, vibration frequency and/or amplitude, and
fluid level. The present invention contemplates that other
operating conditions may also be monitored.
Sensor 14 generates a signal 16. Signal 16 may include a
representation of a single operating condition of container 11.
Alternatively, signal 16 may include a representation of multiple
operating conditions of container 11.
In the rupture disk embodiment illustrated in FIG. 2, a first
pressure sensor 44 may be exposed to the system fluid on the inlet
side of rupture disk 40. As shown, first pressure sensor 44 may be
disposed in inlet safety head 26. Alternatively, first pressure
sensor 44 may be disposed further upstream of inlet safety head 26
or may be attached directly to pressurized container 11. First
pressure sensor 44 generates a signal that is representative of the
fluid pressure exerted on the inlet side of rupture disk 40.
A second pressure sensor 45 may be exposed to the system fluid on
the outlet side of rupture disk 40. As shown, second pressure
sensor 45 may be disposed in outlet safety head 28. Alternatively,
second pressure sensor 45 may be disposed further downstream of
outlet safety head 28. Second pressure sensor 45 generates a signal
that is representative of the fluid pressure exerted on the outlet
side of rupture disk 40.
In addition, a temperature sensor 46 may be exposed to the system
fluid on the inlet side of rupture disk 40. As shown, temperature
sensor 46 may be disposed in inlet safety head 26. Alternatively,
temperature sensor 46 may be disposed further upstream of inlet
safety head 26 or may be attached directly to pressurized container
11. Temperature sensor 46 generates a signal that is representative
of the sensed temperature of the system fluid.
The present invention contemplates that a pressure event sensor 42
may be operatively engaged with pressure relief device 12. In the
embodiment illustrated in FIG. 2, pressure event sensor 42 is a
"burst sensor" that generates a signal when rupture disk 40
activates. The burst sensor may be a "broken wire" burst sensor,
such as, for example, the Burst Alert Sensor manufactured by
BS&B Safety Systems, Inc. The present invention contemplates,
however, that different types of pressure event sensors, such as,
for example, leak sensors, magnetically activated proximity
switches, and pressure switches, that are adapted for use with
different types of pressure relief or control devices may also be
used.
As illustrated in FIG. 2, a pressure event sensor 42 is positioned
on outlet safety head 28. Pressure event sensor 42 includes a wire
43 disposed proximate outlet safety head 28. Wire 43 is connected
to a power source (not shown), which may be, for example, a
battery. The power source and wire 43 form an electrically-powered
circuit that traverses the outlet flow path from rupture disk
40.
When rupture disk 40 ruptures and allows fluid to flow into outlet
pipe 19, the force of the fluid, the shock wave generated in the
piping due to the rupture of the rupture disk, physical contact
with the ruptured disk, or a combination of these events will break
wire 43. In addition, if rupture disk 40 exhibits leakage, the
resulting fluid build-up against pressure event sensor 42 would be
sufficient to break an appropriately configured wire 43. When wire
43 breaks, the electrically-powered circuit changes from a closed
circuit to an open circuit. The opening of the circuit is a signal
that indicates that the pressure relief device has activated or is
leaking.
The present invention contemplates that sensor 14 may be of any
type readily apparent to one skilled in the art. For example,
sensor 14 may be a fluid pH/acidity level sensor, a vibration
sensor, of a fluid level sensor.
As illustrated in FIG. 1, a control 50 is operatively connected to
sensor 14 to receive the generated signal 16. Control 50 processes
signal 16 to identify operating conditions that warrant sending a
warning to an operator, such as when the operation conditions may
impact the operation of auxiliary device 12. Control 50 may
generate a warning when an operator should be alerted to an
operating condition that may impact the operation of the auxiliary
device.
Sensor 14 may send signal 16 to control 50 through a hard-wire
connection. Alternatively, sensor 14 may include a transmitter that
sends a wireless signal 16 to control 50. It is contemplated that
the wireless communication may be an transmission that has a
frequency of between about 902 and 928 MHz. The wireless
communication may occur at any licensed or unlicensed RF frequency
band or at some other acceptable frequency.
The wireless communication may use any one of a number of standard
communication protocols, including, for example: short range
wireless standards and techniques such as bluetooth; 3.sup.rd
generation digital phone service; global system for mobile
communication "GSM"/code-division multiple access "CDMA"; short
message service "SMS"; wireless Ethernet "Wi-Fi"; or wireless
application protocol "WAP." In addition, the wireless communication
may be configured for "frequency hopping," where the frequency that
the wireless communication uses varies between successive
transmissions. The wireless communication may utilize any common
"frequency hopping" algorithm readily apparent to one skilled in
the art.
Control 50 may also be connected to an internal or external memory
58. Control 50 may store a history of the operating conditions
experienced by pressurized container 11 and/or auxiliary device 12
in memory 58. The stored history may be a compilation of raw data
such as a history of sensor 14 sent via signal 16. Alternatively,
control 50 may process signals 16 and store only certain data in
memory 58 that is identified during processing.
Control 50 may include a processor or computer. FIG. 3 depicts in
more detail a computer suitable for use with control 50. As shown,
the computer may have a first memory 60, a secondary storage 62, a
processor 66, such as a central processing unit, an input device
70, and an output 72. The computer may also include a display
device 68. First memory 60 and secondary storage 62 may store
applications, such as application 64, or information for execution
and use by processor 66. The present invention contemplates that
the computer may be connected to a network 74, such as the
Internet.
Although the computer is depicted with various components, one
skilled in the art will appreciate that this computer can contain
additional or different components. Furthermore, although aspects
of the present invention are described as being stored in memory,
one skilled in the art will appreciate that these aspects can also
be stored on or read from other types of computer program products
or computer-readable media, such as computer chips and secondary
storage devices, including hard disks, floppy disks, or CD-ROM, or
other forms of RAM or ROM. These aspects of the present invention
may also include modules, implemented in software, hardware, or a
combination, configured to perform a particular method implementing
an embodiment consistent with the present invention. In addition,
the computer-readable media may include instructions for
controlling a computer system to perform a particular method.
In the embodiment illustrated in FIG. 2, control 50 is configured
to receive signals representative of the operating conditions of
the container and perhaps also the auxiliary device(s) as generated
by the temperature, pressure, and burst sensors. Control 50 is
connected to first pressure sensor through wire 48, to second
pressure sensor through wire 51, to temperature sensor through wire
49, and to pressure event sensor 42 through wire 43. Each of the
sensors may generate and transmit signals representative of their
respective function on either a continuous or periodic basis.
Control 50 receives each signal and processes the signals. The
signals may be transmitted through a hard-wire connection or
through wireless communication to control 50. The present invention
contemplates that that the signals generated by each of the
condition sensors may be transmitted to control 50 through a bus
system, such as, for example, a Fieldbus, Modbus, or a Profibus,
that uses a single two-wire connection to distribute the output
from an array of applied sensors. Control 50 may be programmed to
handle multiple auxiliary devices and pressure containers.
The present invention further contemplates that each of the sensors
and control 50 may include a device configured to both send and
receive signals, such as, for example, a transceiver. This two-way
communication ability may be used to verify that the system is
functioning properly. For example, control 50 may send a signal to
each sensor to determine if the particular sensor is operational.
In response, the sensor may return a signal to control 50 to
provide diagnostic information. Based on the returned signal, or
the lack of a returned signal, control 50 may determined if each
sensor is functioning properly.
As illustrated in FIG. 3, control 50 also includes an input device
70. Input device 70 may be a keyboard or similar device connected
to or integral with control 50. Alternatively, input device 70 may
be a PC or laptop computer that is separate from control 50. Using
input device 70, a user may enter specified performance
characteristics that are relevant to the operation of pressure
relief device 12. Such performance characteristics may include, for
example, the maximum allowable working pressure of the system, the
rated activation pressure of the pressure relief device,
temperature parameters (i.e. high and low temperatures), allowable
back pressures, life cycle information, pressure relief device
material information, and threshold parameters (as described in
greater detail below).
Control 50 processes the monitoring signals provided by each of the
sensors to determine whether an operator should be alerted to the
current or past operating conditions. An operator may need to be
notified when, for example, the operating conditions will impact
the operation of auxiliary device 12 or when container 11 is nearly
full or nearly empty of fluid. For example, in the rupture disk
embodiment of FIG. 2, control 50 will identify a condition or
conditions that may impact the activation pressure of the rupture
disk or its longevity in service. If the operating conditions meet
certain conditions, control 50 generates a warning 54 (referring to
FIG. 1).
In addition, control 50 may be configured to store historical data
relating to the operating conditions of container 11 and the
function of auxiliary device 12 in internal or external memory 58.
In one currently contemplated embodiment, control 50 stores a
series of monitoring signals in first memory 60. The stored
monitoring signals represent the system operating conditions for a
recent period of time, such as, for example, the previous 15
minutes. When new monitoring signals are received, the new signals
are stored in first memory 60 and the oldest signals are deleted
from first memory 60. In this manner, control 50 maintains a record
of the recent operating conditions experienced by auxiliary device
12. Upon receipt of a trigger signal, such as, for example, an
event signal from a pressure event sensor, control 50 may transmit
the history of signals stored in first memory 60 to secondary
storage 62. This history of signals can then be analyzed to provide
information regarding the container operating conditions
immediately prior to the receipt of the trigger signal.
As also shown in FIG. 1, an alerting device 52 may be in
communication with control 50. Alerting device 52 may communicate
with control 50 through a hard-wire connection or through a
wireless communication protocol. The present invention contemplates
that alert device 52 may be any device capable or displaying or
providing the warning generated by control 50. Such devices may
include, for example, computer monitors, light emitting diodes,
sound generating devices, pagers, Internet based services,
processors with integral LCD displays, and mobile phones.
The following discussion generally describes several processing
methods in which control 50 may determine that the operating
condition(s) warrant the generation of a warning message, such as
when the operating condition(s) will impact the operation of the
pressure relief device. These processing methods are described in
connection with the rupture disk embodiment as illustrated in FIG.
2. The present invention contemplates that similar processing
methods may be used in conjunction with other types of safety
devices and/or pressure information providing devices.
Pressure Conditions
The flowchart of FIG. 4 illustrates a first exemplary method 80 of
analyzing sensed pressure signals generated by first pressure
sensor 44. As discussed above, control 50 receives a signal from
first pressure sensor 44 that is representative of the fluid
pressure on the inlet side of rupture disk 40. (Step 82).
Control 50 then determines if the operating pressure ratio of the
disk has been exceeded. (Step 84) The operating pressure ratio of
the rupture disk is exceeded when the pressure sensed by first
pressure sensor 44 is greater than an operating pressure ratio
threshold. The operating pressure threshold is typically defined as
a percentage of the activation pressure of the rupture disk.
Control 50 is programmed to recognize this percentage or its actual
pressure value. Preferably, the information needed to determine if
the operating pressure ratio is exceeded is input to control 50 as
part of the performance characteristics for the particular pressure
relief device during the application set up programming of the
control. If the sensed pressure is greater than this threshold, an
operating pressure warning is generated. (Step 86).
The generated warning may be any type of alert designed to notify
an operator of a potential problem. For example, the warning may be
a message displayed on a monitor, an activated light emitting
diode, a sound alarm, or the activation of a remote device, such as
a pager or a cellular phone. Preferably, the generated warning
includes a message or other indication of the operating condition
that triggered the warning. For example, the operating pressure
warning may include a message such as "Operating Pressure Ratio
Exceeded."
Control 50 also determines if the vacuum capability of rupture disk
40 has been exceeded. (Step 88) A vacuum threshold for the
particular rupture disk may be input into control 50 as part of the
performance characteristics or a default value may be used. If the
pressure sensed by first pressure sensor 44 is below the vacuum
threshold, a vacuum warning is generated (step 89) to alert an
operator to the vacuum condition.
Control 50 also determines if the cycle life of rupture disk 40 has
been exceeded. (Step 90). A "pressure cycle" occurs when the
pressure of the system fluctuates between a lower and an upper
value. The parameters defining the upper value may be input into
control 50 or default values used. When a pre-determined number of
pressure cycles have been experienced, control 50 will generate a
"cycle life exceeded" warning. (Step 91).
The number of "pressure cycles" experienced by rupture disk 40 may
be calculated in several different ways. In one currently
contemplated embodiment, a cycle count will be incremented when
rupture disk 40 experiences a pressure fluctuation from the lower
threshold to upper threshold and back to the lower threshold.
Alternatively, the cycle count may be incremented when rupture disk
40 experiences a pressure fluctuation from the upper threshold to
the lower threshold and back to a upper threshold.
Control 50 may also store a "hysteresis" value for cycle counting
purposes. The "hysteresis" value identifies a pressure change that
may impact the cycle life of the rupture disk but does not meet the
threshold criteria described above. When the rupture disk 40
experiences a pressure fluctuation that is within the upper and
lower thresholds and is greater than the hysteresis value, this
pressure fluctuation may be counted as a cycle. For example, a
rupture disk may have a lower cycle threshold of 75 psi, an upper
cycle threshold of 92 psi, and a hysteresis value of 10 psi. Each
time that the pressure within the system fluctuates by 10 psi but
does not reach either 75 psi or 92 psi, the cycle count may be
incremented. With this approach, all pressure fluctuations that may
have an impact on the cycle life of rupture disk 40 will be
counted.
Control 50 further determines if the dynamic cycle life is
exceeded. (Step 92). The dynamic cycle life is a measure of the
number of times the pressure differential across the disk changes
from negative to positive or from positive to negative. The values
defining the dynamic cycle life may be input into control 50 or
default values may be used. Control 50 maintains a count of the
number of times the pressure sensed by first pressure sensor 44
changes from positive to negative or negative to positive. After a
pre-determined number of changes, control 50 issues a "dynamic
cycle life exceeded" warning. (Step 93).
The flowchart of FIG. 5 illustrates a second exemplary method 100
of analyzing sensed pressure signals from both first pressure
sensor 44 and second pressure sensor 45. As discussed above,
control 50 receives a signal from first pressure sensor 44 that is
representative of the fluid pressure on the inlet side of rupture
disk 40 (step 102) and a signal from second pressure sensor 45 that
is representative of the fluid pressure on the outlet side of
rupture disk 40 (step 104).
Control 50 determines if the operating pressure ratio has been
exceeded. (Step 106). When both the inlet and outlet pressure
signals are received, control 50 determines if the pressure
differential, i.e. inlet pressure-outlet pressure, exceeds the
operating pressure ratio threshold. As noted above, the operating
pressure ratio is determined as a percentage of the activation
pressure of rupture disk 40. The parameters defining the operating
pressure ratio threshold may be input into control 50 or default
values may be used. If the pressure differential exceeds the
operating pressure ratio threshold, an "operating pressure ratio"
warning is generated. (Step 107).
Control 50 may also determine if there is an excessive back
pressure. (Step 110). An excessive back pressure may exist if the
pressure sensed by second pressure sensor 45 is above a certain
level. An excessive back pressure may also exist if the pressure
differential over rupture disk 40 is negative, i.e. the outlet
pressure is greater than the inlet pressure, and the negative
pressure differential exceeds a predetermined limit. Parameters
defining the back-pressure conditions may be input into control 50
or default values may be used. If either of the back-pressure
conditions exist, a "back pressure" warning is generated. (Step
111).
Control 50 may also determine if the maximum allowable working
pressure of the system is being exceeded. (Step 112) As described
previously, rupture disk 40 will activate when the pressure
differential across the rupture disk is greater than the activation
pressure. If a sufficient back pressure is exerted on the rupture
disk, it is possible that the inlet pressure may rise above the
maximum allowable working pressure without activation of the
rupture disk. This condition could place the entire system at risk.
If this condition is detected, control 50 generates a "MAWP
exceeded" warning. (Step 113).
Control 50 also determines if the cycle life is exceeded. (Step
114). A "pressure cycle" may also occur when the pressure
differential over rupture disk 40 cycles between a lower threshold
and an upper threshold. The parameters defining the upper and lower
threshold may be input into control 50 or default values may be
used. After a certain number of pressure cycles are experienced,
control 50 will generate a "cycle life exceeded" warning. (Step
115).
Control 50 may also determine if the dynamic cycle life is
exceeded. (Step 116). As noted above, the dynamic cycle life is
measured as the number of times the pressure differential across
the disk changes from negative to positive or from positive to
negative. Control 50 maintains a count of the number of times the
pressure differential changes from positive to negative or negative
to positive. After a pre-determined number of changes, control 50
issues a "dynamic cycle life exceeded" warning. (Step 117).
Control 50 may also use the information provided by the pressure
and temperature sensors to drive a controlled safety pressure
relief system ("CSPRS"). If the monitored conditions indicate an
impending over-pressure condition, control 50 may activate the
CSPRS to alleviate or prevent the over-pressure condition. The
activation of the CSPRS may result in the opening of a control
valve that injects a chemical reaction agent, catalyst, or
stabilizer into the working fluid or in the activation of a valve,
such as, for example, a butterfly valve or globe valve, that will
allow the release of fluid in a sufficient quantity to avoid or
limit the over-pressure or under-pressure condition. Control 50 may
also generate an appropriate warning to alert an operator to the
activation of the CSPRS.
Temperature Conditions
The flowchart of FIG. 6 illustrates an exemplary method 120 of
analyzing sensed temperature signals generated by temperature
sensor 46. As discussed above, control 50 receives a signal from
temperature sensor 46 that is representative of the fluid
temperature on the inlet side of rupture disk 40. (Step 122).
Control 50 determines if the design temperature is exceeded. (Step
124). The design temperature is exceeded if the sensed temperature
is greater than an upper threshold or is less than a lower
threshold. These thresholds may be input into control 50 or default
values used. Under either condition, control 50 will generate an
"excessive temperature" warning. (Step 126).
Control 50 may also determine if the temperature of the fluid in
the system will affect the activation pressure of rupture disk 40.
(Step 128). The activation pressure of rupture disk 40 may be
affected if the temperature of the fluid in the system deviates
from a certain limit. The type of material used in rupture disk 40
may be stored in the memory of control 50 along with a
pressure/temperature curve for the particular material. The
pressure/temperature curve identifies the amount of change in the
activation pressure of the rupture disk over a range of
temperatures. If control 50 determines that the current temperature
of the system will increase the activation pressure of the rupture
disk by a certain percentage, such as, for example, 5%, an
"activation pressure affected" warning is generated. (Step
130).
Control 50 may also determine if the temperature of the fluid in
the system will affect the service life of rupture disk 40. (Step
132). The service life of rupture disk 40 may be affected if the
temperature of the fluid in the system is above a certain limit. A
higher than expected temperature may cause the rupture disk to
activate at a lower pressure, or pressure differential. Control 50
uses the stored pressure/temperature curve for the particular
rupture disk material to determine if the activation pressure of
the rupture disk will be decreased by a certain percentage, such
as, for example, 5%. If this condition exists, control 50 generates
a "service life affected" warning. (Step 134).
It is contemplated that control 50 may use a combination of the
pressure and temperature determinations described above to identify
additional conditions that would require a warning to be generated.
For example, if the fluid temperature in the system rose to a limit
that would result in a decrease in the activation pressure, control
50 may use the decreased activation pressure as the basis for
operating pressure ratio threshold calculation. In this scenario,
the operating pressure ratio threshold would be also be decreased
to account for the decreased activation pressure. The decrease in
the operating pressure ratio threshold may be proportional to the
decrease in activation pressure.
Activation Conditions
Control 50 may also generate one or more warnings in response to
received signals that indicate rupture disk 40 has experienced a
pressure event, such as, for example, activation or leaking. As
described in greater detail below, these conditions are identified
by signals received from one or more of pressure event sensor 42,
first pressure sensor 44, and second pressure sensor 45.
When control 50 receives a signal from pressure event sensor 42
that the rupture disk has activated, control 50 verifies that the
activation signal is accurate. Control 50 will verify that the
sensed pressures on the inlet side and/or the outlet side of
rupture disk 40 support the activation signal. For example, a
condition where the outlet pressure is at or near atmospheric
pressure might indicate that the activation signal was erroneous.
In addition, a condition where the inlet pressure does not drop in
accordance might also indicate that the activation signal was
erroneous. Control 50 may generate a warning to indicate that an
activation signal was generated from pressure event sensor 42, but
that the pressure readings do not support the activation signal. If
the pressure readings do support the activation signal, i.e. the
inlet pressure drops and the outlet pressure rises, control 50 may
generate a warning that the rupture disk has activated.
Control 50 may also identify a condition where rupture disk 40 has
activated, but no activation signal was provided by pressure event
sensor 42. This condition may occur in the case of a low pressure
rupture, where the fluid flow is not great enough to trigger
pressure event sensor 42. This condition might be identified by a
drop in inlet pressure accompanied by a rise in outlet pressure. If
this condition is detected, control 50 will generate an appropriate
warning.
Additional Conditions
Control 50 may also identify additional conditions, such as a
suspected rupture disk malfunction. Some rupture disks have a
damage ratio that is greater than 1. This indicates that a damaged
rupture disk will activate at a pressure that is higher than the
rated activation pressure. Control 50 may identify this condition
when the inlet pressure or pressure differential, as sensed by
first pressure sensor 44 and second pressure sensor 45, exceeds the
rated activation pressure by a certain percentage, such as, for
example 110%. When this condition is identified, control 50 will
generate an appropriate warning.
Control 50 may also alert an operator when container 11 is nearly
full or nearly empty of fluid. A sensor, such as, for example, a
pressure switch or a pressure indicator, may be connected to
container 11 to monitor the fluid level within the container. When
the sensor determines that the fluid level in container 11 is
approaching a maximum or a minimum, the sensor may send a signal to
control 50 indicate an impending over-pressure or under-pressure
condition. The signal may be transmitted to control 50 through the
wireless communication system described previously. Upon receipt of
the signal, control 50 may generate an appropriate warning for the
operator. The operator may then open a supply valve to replenish
the fluid supply in container 11 or shut of a supply valve to stop
the flow of fluid to container 11. For example, if container 11 is
used to feed a process, control 50 may generate a warning when the
fluid level within container 11 is nearly depleted. Similarly, if
container 11 is receiving fluid from a supply tank, control 50 may
generate a warning when container 11 has received its required
supply of fluid. It is also contemplated that control 50 may be
integrated with the supply system to automatically close or open
valves to relieve or prevent the over-pressure or under-pressure
condition.
As will be apparent from the foregoing disclosure, the pressurized
container monitoring system of the present invention provides
warnings to alert an operator to potential problems based on the
operating conditions of the pressurized container. These problems
may be based on the operating conditions experienced by a safety
device or an information-providing device. The system and method of
the present invention alerts the operator to the problems so that
the operator may take corrective action, such as the repair or
replacement of the particular device. In this manner, the present
invention ensures the integrity and operation of the pressurized
system.
It will be apparent to those skilled in the art that various
modifications and variations can be made in the method of
manufacture of the present invention and in construction of the
pressurized container monitoring system without departing from the
scope or spirit of the invention. Other embodiments of the
invention will be apparent to those skilled in the art from
consideration of the specification and practice of the invention
disclosed herein. It is intended that the specification and
examples be considered as exemplary only, with a true scope and
spirit of the invention being indicated by the following
claims.
* * * * *